Next generation networking and computing systems need compact and cost-effective devices to be promoted to the market. At microwave and higher frequencies, distributed-element filters and other devices are necessary. As a cost-effective approach, multilayer board technologies can be applied to design such devices. These technologies can realize a three-dimensional design concept and, as a result, improve compactness of elements forming the systems.
One type of structures, being used as a building block in distributed-element components, is resonant open-circuited and short-circuited stubs which are applied to design the components. Usually, these stubs in multilayer boards are formed as open-circuited or short-circuited planar transmission line segments. In this case, parasitic coupling, unwanted radiation and large enough dimensions can be those issues, which can arise at development of distributed-element devices.
Japanese Laid Open Application JP 2008-507858 (US 2008/0093112A1) discloses that composite via structures, used to obtain both three-dimensional open-circuited and short-circuited shield stubs, are formed in multilayer boards in which additional smooth plates connected to the signal via are used to control the characteristic impedance of the stub. Also, ground vias around the signal via structure are applied to improve the quality factor (Q-factory of such composite via structures. Application of such composite via structures gives a possibility to form high-performance filtering components in multilayer boards.
However, in many applications, dimensional reductions of filtering structures in a multilayer board filled in a fixed material are necessary.
Also, it is important to improve sharpness of the passband and stopband in filtering components to satisfy requirements of designing systems.